Numerical Analysis On Hydrodynamic Performance Of Catamaran In Large Waves

It is one of key issues to predict the seakeeping performance accurately in ship design. When a ship is advancing in waves, series of strongly nonlinear phenomena make the problem much more complex, such as the added resistance introduced by heave and pitch motions, and the green water etc. Methods to predict hydrodynamic forces and ship motions in naval engineering are divided into two categoris, namely, the physical experiments and numerical simulation. The physical experiments are the most reliable, but with low efficiency and high cost. The traditional numerical calculation methods are based on the potential-flow theory which is hard to take the viscosity and nonlinear effects into account. In contrast, the computational fluid dynamics(CFD) based on the viscous-flow theory has captured comprehensive attention due to its effeciency of handling nonlinear viscous free-surface flow problems. On the basis of sufficient investigation and summary of the research progress on ship motion response and added resistance, the present research has been carried out as follows:Firstly, a 3-D numerical wave tank is established based on CFD software FINE/Marine, which is developed for simulating nonlinear viscous flows around th e ship by solving the Reynolds-average Navier-Stokes(RANS) equation with k- ω(SST-Menter) turbulence model. After systematic convergence studies, the steady waves generated by a standard Wigley hull are simulated. The computed wave profile, wave pattern, pressure distribution and wave-making resistance are compared with experimental measurements in a good agreement.Then, the forward-speed radiation problems of Wigley hull are simulated. The forced heave and pitch are simulated and computed results incl uding the added mass and damping coefficients are in good agreement with the experimental data. Besides, the diffraction problem of Wigley hull fixed in waves is simulated, the computed exciting forces are presented to validate the efficiency of the numerical model.Next, the ship motion and added resistance of Wigley hull with motion free in both linear and nonlinear waves are calculated and compared with experimental data of linear waves. The differences are discussed and analyzed to provide an indication about nonlinear effects.Finally, the steady waves generated by a Wigley catamaran are simulated. The calculated wave-making resistance shows a satisfactory agreement with measured data. As well, the ship motion and added resistance of the Wigley catamaran in linear and nonlinear waves are simulated. A comparison of results between the monohull and catamaran is carried out and it is confirmed that the catamaran has a higher seakeeping performance than the monohull.According to above results and comparisons, it is confirmed that the present numerical model has the capacity of evaluating the seakeeping performance of catamaran in breaking waves and simulating the viscous free surface flow around the ship with favorable accuracy. It has the potential to be a pplied to wider hydrodynamic analysis of more ocean and offshore structures.